(1) Field of the Invention
The present invention relates to a node apparatus and packet communication method in a packet communication network. More particularly, the invention pertains to a node apparatus and packet communication method in a packet communication network through which communication with a mobile terminal is carried out.
(2) Description of the Related Art
Recent years have seen a significant increase in traffic in a packet communication network based on the Internet Protocol (IP) because of the widespread proliferation of World Wide Web (WWW) applications. In the Internet, a node apparatus for interconnecting networks is provided with a routing table which is updated according to the IP routing protocol, and the routing table is referred to based on a destination IP address contained in a header of a received packet in order to determine an outgoing path for the received packet.
Conventionally, functionality for supporting mobile terminals in the Internet is unsatisfactory, and therefore the Internet is primarily used for communication between stationary terminals. In order for a mobile terminal to carry out IP packet communication with another stationary or mobile terminal, a connection must be pre-established between the mobile terminal and a network stationary server (e.g., PPP server) according to the Point-to-Point Protocol (PPP) or any other data link layer protocol so that the network stationary server can work as a router.
Since the above-mentioned conventional method is based on the premise that the mobile terminal is connected to the stationary server prior to IP packet communication, no problem occurs in a situation where the mobile terminal starts originating communication with another stationary terminal. However, in a situation where it is attempted to start communication with the mobile terminal used as a destination, IP packets cannot be sent to the mobile terminal since the mobile terminal is not yet connected to the stationary server at the start of communication. That is to say, unlike conventional telephone communication, the prior art met hod mentioned above does not provide support functionality for allowing the start of communication by calling (paging) a mobile terminal to be accessed as a destination.
A variety of schemes based on the ITU IMT-2000 have been proposed for realizing a network architecture in which it is allowed to call a destination mobile terminal for IP packet transmission thereto as in the conventional telephone communication. As a representative scheme thereamong, ETSI “GSM03.60 Stage-2 Service Description of the General Packet Radio Service (GPRS)” is found.
A packet switched network based on the GPRS scheme comprises subscriber exchanges and gateway exchanges as in a conventional telephone switching system network. In the packet switched network, an origination terminal (stationary or mobile terminal) calls a destination mobile terminal through a signaling procedure similar to a conventional telephone call control procedure, and then the origination terminal sends IP packets to the destination mobile terminal.
Where mobile terminals are used at both the origination and destination points, IP packets are transmitted to an origination home gateway exchange (origination home agent node) located in a home area of an originator (origination mobile terminal) through a visitor subscriber exchange (origination node) located in a visitor area of the originator. At this step of operation, the origination visitor subscriber exchange (origination node) adds a new header (encapsulation header) to each IP packet received from the origination mobile terminal, and then the received packet is sent to the origination home gateway exchange (origination home agent node) in a tunneling method.
The origination home gateway exchange removes the encapsulation header from the received packet (decapsulation), and the origination home gateway exchange identifies a destination home gateway exchange (destination home agent node) of a recipient (destination mobile terminal) according to a destination IP address contained in a header field of each original IP packet. The origination home gateway exchange also adds a new header (encapsulation header) to each received IP packet, which is then sent to the destination home gateway exchange in the tunneling method.
The destination home gateway exchange decapsulates the received packet, and based on a home IP address of the destination mobile terminal indicated by the IP address contained in the header field of each original IP packet, the destination home gateway exchange makes reference to a home location register in which information on the current location of the destination mobile terminal is stored. Thus, a destination visitor subscriber exchange (destination node) corresponding to the current location of the destination mobile terminal can be identified. When the destination visitor subscriber exchange which allows communication with the destination mobile terminal is identified as mentioned above, the destination home gateway exchange encapsulates the IP packet, which is then sent to the destination visitor subscriber exchange for the recipient in the tunneling method. The destination visitor subscriber exchange for the recipient decapsulates the received packet to obtain the original IP packet. Then, the original IP packet is transferred to a connection port connected with a wireless base station which covers the current location of the destination mobile terminal.
A section of communication between a sending node which encapsulates IP packets and a receiving node which decapsulates the encapsulated packets to obtain the original IP packets is commonly referred to as a tunnel. In the above example of packet communication between mobile terminals based on the GPRS scheme, a total of three tunnels are formed between the origination visitor subscriber exchange and the origination home gateway exchange, between the origination home gateway exchange and the destination home gateway exchange, and between the destination home gateway exchange and the destination visitor subscriber exchange.